1. Field of the Invention
The present invention relates to a fluorescence sensor for measuring a concentration of an analyte and, more particularly, to a fluorescence sensor, which is a micro-fluorescence spectrophotometer, manufactured using a semiconductor manufacturing technique and an MEMS technique.
2. Description of the Related Art
Various analyzers for checking presence of an analyte, i.e., a substance to be measured in liquid or measuring a concentration of the analyte have been developed. For example, there is a known fluorescence spectrophotometer for injecting a fluorescent pigment, which changes in characteristics because of the presence of an analyte and generates fluorescent light, and a solution to be measured including the analyte into a transparent container having a fixed capacity and irradiating an excitation light E to measure fluorescent light intensity from the fluorescent pigment to thereby measure the concentration of the analyte.
A small fluorescence spectrophotometer includes a photodetector and an indicator layer containing a fluorescent pigment. When the excitation light E from a light source is irradiated on the indicator layer into which the analyte in the solution to be measured can penetrate, the fluorescent pigment in the indicator layer generates fluorescent light with a light amount corresponding to the analyte concentration in the solution to be measured. The photodetector receives the fluorescent light. The photodetector is a photoelectric conversion element. The photodetector outputs an electric signal corresponding to the light amount of the received fluorescent light. The analyte concentration in the solution to be measured is measured from the electric signal.
In recent years, in order to measure an analyte in a micro-volume sample, a micro-fluorescence spectrophotometer manufactured using the semiconductor manufacturing technique and the MEMS technique has been proposed. The micro-fluorescence spectrophotometer is hereinafter referred to as “fluorescence sensor”.
For example, a fluorescence sensor 110 shown in FIGS. 1 and 2 is disclosed in U.S. Pat. No. 5,039,490. The fluorescence sensor 110 is configured by a transparent supporting substrate 101 through which excitation E can be transmitted, an optical tabular section 105 including a photoelectric conversion element section 103 configured to convert fluorescent light into an electric signal and a light-condensing function section 105A configured to condense the excitation light E, an indicator layer 106 configured to interact with an analyte 9 to thereby generate fluorescent light through incidence of the excitation light E, and a cover layer 109.
The photoelectric conversion element section 103 is, for example, a photoelectric conversion element formed on a substrate 103A made of silicon. The substrate 103A does not transmit the excitation light E. Therefore, the fluorescence sensor 110 includes, around the photoelectric conversion element section 103, an air gap region 120 through which the excitation light E can be transmitted.
That is, only the excitation light E transmitted through the air gap region 120 and entered the optical tabular section 105 is condensed to the vicinity of an upper part of the photoelectric conversion element section 103 in the indicator layer 106 by the action of the optical tabular section 105. Fluorescent light F is generated by interaction of condensed excitation light E2 and the analyte 9 penetrating into an inside of the indicator layer 106. A part of the generated fluorescent light F enters the photoelectric conversion element section 103. A signal of an electric current, a voltage, or the like proportional to fluorescent light intensity, i.e., the concentration of the analyte 9 is generated in the photoelectric conversion element section 103. Note that the excitation light E does not enter the photoelectric conversion element section 103 by the action of a filter (not shown in the figure) that covers the photoelectric conversion element section 103.
As explained above, in the fluorescence sensor 110, on the transparent supporting substrate 101, a photodiode which is the photoelectric conversion element section 103 is formed on the substrate 103A in which the air gap region 120, which is a passage of the excitation light E, is secured. The optical tabular section 105 and the indicator layer 106 are laminated on an upper side of the substrate 103A.